This historical novel by master-of-the-genre Mary Renault is set in the turbulent world of fourth-century B.C. Greece and Sicily. Nikeratos, a tragic actor, carries with him a gold mask of Apollo that is both his conscience and a reminder of the past golden age. Nikeratos encounters Plato and his friend Dion in the city of Syracuse, as the philosophers try to persuade the tyrant Dionysios to accept the rule of law.  (GRE224, $14.95)